If you’re using Firefox 4, head over to the demo site to see the mashup in action. Other browsers won’t work, but the demo movie below shows how the guitar tab player works.

The reason this experiment only works in Firefox is because it uses Mozilla’s new Audio Data API, which gives web developers a way to interact with raw audio data in HTML5′s <video> and <audio> elements using JavaScript. With the Audio Data API, developers can read and write audio data within the browser, opening the doors for online tools like spectrum analyzers, audio remixing tools and 3D audio visualizations.

While Mozilla’s Audio Data API hasn’t been blessed by the W3C just yet, plenty of what we use on the web right now — XMLHttpRequest anyone? — started out exactly the same way. Because the web embraced XMLHttpRequest, it became a standard. Given this awesome experiment and some of the other great demos we’ve seen that use the Audio Data API, we’re really hoping the W3C adds the Audio Data API to the spec.